LM4 ignition issue

[Bazil]

Hi folks;

I've been struggling with plug fouling for a while now,  had my Dyna die at an early age recently, and have been trying to get to the bottom of it. The carbs have been gone through and I can't see anything outstanding, but did re-set float height to the LHS carb and made sure the choke wasn't hanging.

Just because I had them I replace brushes ( only half worn) and rectifier with brand new. It's also had 5 ohm Dyna coils recently. New plug leads when I did a refresh 5 years ago. Currently running points. New plugs.

If I put a timing light on the bike the RHS looks pretty good and so does the LHS, but the latter at idle only. When I rev it above 2000 RPM the timing light does not fire on the LHS. (RHS is fine at revs)  On a road test the ( probably highly unreliable) voltmeter sits a bit below the 14V mark ( headlight on) at moderate revs but seem to drop down to about 13.2 V as revs rise, sometimes ducking under 13 V.

I have a replacement Dyna sensor ( courtesy Perazzimx14  - what a great guy!), but I dont want to change out the points until I get to the bottom of this.

I was thinking maybe wonky old points, but that wouldn't  explain dying Dyna.

What's going on ?Any thoughts from those more experienced in electrickery?

thanks

Baz

[Old Jock]

Hi Bazil

Weird sorta problem

I think you need to split out this into 2 separate issues and investigate one at a time, it would appear that you may have something strange going on with the both charge and ignition circuits

I'd start with the charging circuit, I'm not saying the problems aren't inter-related they could be I suppose, but solving one at a time would be the approach I'd take

14V sounds about right but it's odd that the charge drops, I'm wondering what sort of reg/rec is on the bike.

So obvious first check the earths on alternator, reg/rec and and main earth from battery to frame, an additional earth strap on the regulator and rectifier won't do any harm either

I ass-ume battery standing volts are good, if the battery is suspect or in a low state low state of charge you could get all sorts of strange results.

Next I would try to full field flash the alternator to make sure it's good. I'll explain more on that later, but I'd prefer others to some in first with opinions and suggestions

If Wayne Orwig or Kiwi Roy come on listen carefully these guys have forgotten more than I'll ever know

John   

[guzzisteve]

I would check contact between point and mount plate, especially if it's been sitting in a box for years.

[Kiwi_Roy]

If I put a timing light on the bike the RHS looks pretty good and so does the LHS, but the latter at idle only.

Carl's schematic shows 2 coils with 2 sets of points and I assume 2 condensers although it doesn't show them. MG Cycle list them for this bike.
The loss of spark off idle sounds like a bad condenser, I just went through that, find a couple of old ones at a wreckers yard. The condensers act with the coil to form a resonant circuit which will almost double the spark strength.

Or is it just that the light is not working as it should?
John is more familiar with those old girls than I am

All I can suggest for the alternator is measure the Voltage across the rotor or better yet the current in series with it to see if it shows loss of field with revs.
I had a California II it would get some sort of a film on the slip rings that caused the current to fall back, if I cleaned them it would boost the current for a week or two
Tell us what brand/model of regulator/rectifier you are running.

[wirespokes]

I like the condenser idea. Try swapping condensers and see if the problem migrates to the right side.

Are the plug wires solid core? Have you checked resistance of the wires and plug caps?

Are both plugs fouling or just the left side?

I'm running 3ohm Dyna coils in the 87 LM - it came to me that way 15K ago. It's also got a Dyna. The 5 ohm coils won't put out as hot a spark as the 3 ohm.

On the charging system - I've had issues before with the alternator slip rings getting a build up of carbon or something on them. Copper cleaner fixed it.

[Bazil]

Thanks for the replies. Haven't had time to check a couple of those yet but :

 - condenser to LHS was changed with new ( just anything I could find at the local auto store) I would be unlucky to have two dud ones!
 - plug wires are stranded copper
 - plug fouling only to LHS
 - Guzziology suggest a dull build up on the slip rings is a good thing, so haven't tried cleaning them as yet
 - rectifier in Bosch ( and new)
 - regulator is Bosch and original
 - battery, while not brand new , is only six months old and seems strong going by cranking speed
 - the timing light is only a cheap Chinese one, but works OK on the RHS; I'm guessing that may not be the culprit but might indicate something.

I'll try to get into the shed during the week to check out some of those possible earth concerns.

Thinking further - what if it's a weak spark which isn't inducing enough current to trigger the ignition light? The bike does not seem to be running on one cylinder, it actually runs reasonably well. Maybe a weak spark is still firing but not delivering enough juice to burn the full charge of fuel ?

What's likely to cause that weak spark? Condenser is a good pick, but that's been replaced. Checking earthing of condenser might be a good idea when I'm checking earths elsewhere. Coil ? They are only months old, but could be - need to check that too ( or do a swap to see if the problem changes side)

Keep the theories coming !

many thanks

Bazil

[Chuck in Indiana]

Just because it's a new condenser, it doesn't mean it's a good condenser. Swap em around anyway, just to rule that out. Just because it's a new plug doesn't mean it's a good plug, either. I have a spark plug tester, and have had two bad ones out of the box. Happened to be Champion both times, which I won't buy any more. A bad plug will do exactly what you are experiencing.
It's probably carburation. 

[wirespokes]

Chuck's right - and it's common knowledge that condensers can be a problem. Everyone will tell you not to swap out an old one for new as the new one could be bad. If it's working, leave it!

And don't ever assume that a new part can't be bad!

Chuck - the float level could be too high, but there's also the fact the timing light is showing no, or weak, spark at higher RPM.

I know, Guzziology does say that about build up on the slip rings, but I had to be rescued once with a dead battery. Cleaning the slip rings got the charging system up and going again. That was the only thing changed, so I'm absolutely certain of the cause and effect.

[Kiwi_Roy]

- Guzziology suggest a dull build up on the slip rings is a good thing, so haven't tried cleaning them as yet
 

Yes, this is what we were taught as apprentices as well, the dull finish on commutators and slip-rings is very hard and will last for ever.
What I'm talking about is some other layer, I thought it might be more of an oily film from a leaking seal perhaps. You could try a solvent like acetone on a cloth to clean slip rings and brushes to see if it makes a short term improvement.

A bad condenser will cause the spark to cut out with any throttle at all, I just went through installing a fake one on my Eldorado, it would barely run.
I only have one common to both sides, you have two so one side could be quite normal.
The condenser is not to prevent sparking at the points as many think, it actually tunes the coil so it rings like a bell electrickery wise.
 

[kfz]

Get rid of the points and fit the dyna,  I see little point in getting the points to wotk which may well me your problem only to swap it out for the dyna.
Sounds a lot like your are suffering cheap unreliable condenser issues.

I'd ditch the points and at least your working toward your end game.

Kev

[wirespokes]

The dark color on the slip rings may be some sort of hard protective coating that develops over the years, but don't think they come that way new.

I had the idea in my instance the brushes were very old and disintegrating, leaving some sort of film on the slip rings. Cleaning that off without removing the dark color may be the best way to go, but I knew no better.

Condensers - they can fail in so many different ways they can mimic just about any other symptom, electrical or fuel related. I've never tried this, but I've heard that the condenser can be removed from the circuit and the engine will run, though the points will pit in short order. Something to remember for test purposes or in an emergency situation.

[Old Jock]

I know less about points issues as I have an electronic system on mine a Sachse and it works well but was problematic at the outset.

However I do remember a thread a long time back where Rodekyll and me were having a debate about the condensers and a lot were stating that the condensers did little with the ignition system in terms of forming part of a resonant circuit, so there purpose was only to reduce the spark across the points. I'm still unsure if that's correct or not. If it is then the plugs will still fire without the condensers, they'll just wear the points in short order.

If it was mine I'd also just stick on the Dyna, but I'm a believer in electronic ignition but that's pretty hotly contested on here and a lot of polarized views on the issue.

Anyways regarding the slip rings I cleaned mine with alcohol when replacing the brushes, mine had a significant build up of God knows what. It cannot do any harm, but I'd be more wary about taking a stone (or any form of abrasive) to them, personally I would not do that on my bike. If the brushes were bouncing or lifting as revs increased you could well start to see odd thing happening I suppose.

After cleaning the brushes my approach would be to start working my way through the charge system, sort it out then move into the ignition

Oh and swapping stuff across to determine if the fault moves is a good approach too. Lot's of good advice in here so far

John

[Kiwi_Roy]

A couple of pictures I took with the scope
First of all I must apologise for not having the scope triggered properly, I only had a minute to grab it.

I have some better pictures to share when iPhoto will let them go


With a good condenser just clipped in place


Unclipping the condenser the Voltage dropped significantly and it seemed to lose definition.

Over the next few days I will try and get some cleaner pictures.

I agree if you have electronic ignition working it's probably going to be more reliable

Roy

[Old Jock]

So if I'm reading that right Roy the condenser/capacitor does form some sort of resonant circuit to boost the voltage?

My gut feeling was that it did, but I had nothing too back it up with

John

[wirespokes]

That's been my understanding too, John, though it also keeps the points from pitting.

[Bazil]

Thanks for all the responses guys.
Haven't got back into the shed yet, but I've got a few things to try now.

Ultimately I want to go back to the Dyna ignition, but I want to make sure that the early demise of the old one wasn't caused by something else in the charge / ignition circuit.

My gut feel is that, while a crook condenser seems the most likely culprit, I've had an old one and a new one one in and the problem persists. I will swap them over side to side however.

If the death of the Dyna is due to something in the ignition system it will not be condensers, as they are taken out of the circuit when the dyna is installed. In a points system condensers are vital - I had a loose one a few years back  ( pre Dyna) and not having it earthed made performance at high revs terrible. Took a while to pinpoint the problem, but once it was screwed to the dizzy body properly ( with Loktite) the mis-firing was cured.

The search for spark continues....

[Old Jock]

There isn't much to the ignition system Bazil

I mean what is there?

Take off at the ignition switch, through the kill switch and then that pos feed splits into 2 and supplies the coils, anything after that is taken care of by either the Dyna or the points system.

The only 2 things that spring to mind that could result in premature demise of a Dyna would be badly earthed/ground/frame connection on the Dyna or plugs and low resistance coils. You are running 5 Ohm coils which are absolutely fine.

One of the reasons I thought to look at charge first is, if the supply circuit is unreliable or suspect then there is a possibility of spikes being introduced or Voltage varying wildly and the Dyna would probably not take to kindly to that.

John

[Bazil]

Just thought I'd give everyone an update and some closure.

Did a bunch of tests :

 - resistance from plug cap to earth 17.5 K ohms both sides ( thought it should be in range of 5 to 8 K?)
 - rectifier to earth OK
 - regulator to earth OK
 - earth from battery to frame OK
 - stator resistance across terminals within spec of 0.38 ohms +/- 10 % OK
 - checked power to both coils OK
 - earth to coils OK
 - field flashed terminal on alternator stator
 - checked carbie float height. I did this originally when I overhauled carbs years ago, but was obviously wrong. Carb height way too high, causing over-fuelling.

After all that, I got the  timing light cutting out on LHS at 4000 RPM ( it did do it at 2000 RPM previously). Voltmeter did however show charging up to 14 V mostly but inexplicably dropping back to 13 V during on road running. Plug chops showed better fuelling.

Then :
 - installed new regulator
 - replaced points. The LHS points did not look like each side met cleanly  and there was a fair bit of play vertically between each side of the LHS point.

Gina now runs much better, with smoother running at lower revs and better acceleration. Hopefully fuel consumption improves too. Heated handgrips now up and running too - these shut down after 5 minutes previously, presumably because battery charge was not capable of supporting them. Voltmeter still occasionally drops back to 13 to 13.2 V, but is mostly just under 14V - I'm writing that off as dodgy a 30 year old voltmeter and / or italian wiring.


 As Chuck says Ignition problems are usually carburation and carburation issues are usually ignition. I think I had both !

I'm ready to put in the replacement Dyna sensor Perazzami gave me, now that everything seems to be working correctly.

So my issues seemed to be rectified ( ha!) by adjusting carb float height, field flashing the stator and replacing the regulator ( and the points). The plug fouling was caused by high float height and the dodgy point I believe and the regulator may have contributed to the Dyna failure ( or not).

I am still hazy on setting float height though. The Dellorto manual gives a different ( greater) height than the workshop manual but neither seems to say what is meant to be happening at that height. I have assumed that at the Dell'orto recommend setting, there should be no fuel flow - that gives the lowest float level. Haven't seen any fuel starvation at high revs, so I guess it's OK

Thanks to everyone for your suggestions and Perazzami for the spare Dyna senor plate

Bazil

[Tom]

Bazil,

Do you have the '87 LM IV SE model?  Red and white?

[Kiwi_Roy]

I seem to have lost my osciloscope pictures, I can tell you from recent experience condensers have a huge effect on spark. it may run without at idle but not when the revs are up
the spark without a condenser is only about 60% and very rough looking.
Don't trust a new condenser, the Chinese will knock off anything like that except they are only interested in your money not your future business.



BTW
It seems that IMG are the latest ones to put the bite in us for hosting our images
This one worked for a few hours, when I pulled the end off the roll fell out, there were no connections to either wire.

[Bazil]

Hi Tom;

mine's a 1986 all red Mark IV ( because they're faster of course )

And you're right Roy - could still be a brummy condenser as well.

Baz

[Kiwi_Roy]

Swap the ones you have from side to side you will see if one is bad.
The one I pictured was on a single coil Eldorado, started out on a ride ok but then after a while started to miss like crazy and barely run, not at all with any significant throttle.
I was lucky to make it home.
I put another one in parallel and it was fine, proving to me that it was open circuit. Hen I filed the crimp off the end the silver foil coil fell out.
Looked perfect but no writing on it at all.
Strange to say the new gauge bezels I bought from the same supplier were useless also, impossible to fit and made of stainless which is too hard to crimp.
The points are still working but again no identifying marks.

[Tom]

Hi Tom;

mine's a 1986 all red Mark IV ( because they're faster of course )

And you're right Roy - could still be a brummy condenser as well.

Baz

Turns out after having rebuilding the carbs 3 different times and checking the electrical parts.  My '87 LM IV SE had the left carb accel pump set wrong.  It was putting 3 times the amount of gas into the left cylinder than the right.  The paint on the accel pump screws showed that it was still in the oem setting from the factory.  I reset it to match the right side and the problem was cured. 

Since I had other Guzzis to ride, it did take a period of time to fix.    It was very frustrating. 

I check accel pumps on the carbs now if it's "ignition" related.

[Kiwi_Roy]

Good feedback 

As a Sparky I automatically assume the problem is electrical, not the first time I have been wrong.